From the given graph, let's assume that a third of MK is measured to be 26.
A segment bisector cuts a segment into two equal parts. In other words, a segment bisector is in the middle of a segment.
As shown in the given graph, JK appears to be the Segment Bisector.
Let's determine the length of MN,
MK = KN
MK + KN = MN or 2MK = MN
1/3 MK = 26
MK = 26 x 3
MK =78
2MK = MN
2(78) = MN
156 = MN
MN = 156
Therefore, the measure of MN is 156.